Put the cubed sweet potatoes in a saucepan with enough water to cover. Bring to a boil, then reduce heat, cover and simmer until fork-tender.
Transfer cooked sweet potatoes to a mixing bowl and add salsa, chili powder, lime juice, and nutritional yeast. With a fork, smash and mix until well-combined. Fold in black beans. Add salt and pepper to taste.
Heat a grill or grill pan over medium heat. Spread a heaping ½ cup of the sweet potato mixture onto a tortilla. Top with a second tortilla and gently press it down. Repeat with remaining tortillas.